C100DEV MongoDB Overview and Document Model Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  db.collection.find({ $elemMatch: { 'address.city': 'New York' } })

  Why it's wrong here

  The `$elemMatch` operator is designed to match elements within an array. Since `address` is a nested document, not an array, using `$elemMatch` here is inappropriate and would not match any documents. It would only be useful if `address` were an array of subdocuments. Therefore, this query fails to retrieve the desired results.

• ✗

  db.collection.find({ address: { city: 'New York' } })

  Why it's wrong here

  This query uses an exact match on the entire `address` subdocument. It would only return documents where the `address` field is exactly `{ city: 'New York' }`, meaning no other fields like `street` or `zip` are present. Since the actual documents have additional fields in the nested document, this query would not match any of them.

• ✓

  db.collection.find({ 'address.city': 'New York' })

  Why this is correct

  This query uses dot notation to target the `city` field within the nested `address` document. It correctly matches documents where the nested `city` value is 'New York', regardless of other fields in the subdocument. Dot notation is the standard way to query nested fields in MongoDB, allowing precise access to embedded document properties.

• ✗

  db.collection.find({ address.city: 'New York' })

  Why it's wrong here

  This syntax is invalid in MongoDB. When querying nested fields, the field path must be enclosed in quotes if it contains a dot, like `'address.city'`. Without quotes, the JavaScript parser would interpret `address.city` as an attempt to access a property of an object, leading to a syntax error or unexpected behavior. The correct approach uses a string with dot notation.